FB DISCUSSIONS: HSRP vs STP


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HSRP vs STP: Good One ..
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Asked in NETWORK SPECIALIST Interview .. !!
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Scenario
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==> We have two routers A & B, in a HSRP group. A is active, B is standby. In normal scenario, trafffic will pass through active router, A.
==> Now, STP came into the picture. As per configuration in STP, B is acting as the Root bridge.
==> So, what will happen ?
Traffic will pass from router, A or B ?
 

Like· ·

  •  
    Rahman Iqbal hmm….great.
    20 hrs · Like · 1

     

  •  
    Dheena Dayalan if Root bridge and HSRP active are in different switch, This creates non-optimal traffic paths which can lead to higher congestion on the inter-core-switch trunk
    but still it will work i hope
  •  
    Sumit Sharma Dheena Dayalan .. u got it right .. This is not a good design, actually we are just discussing the concept & doing analysis of scenario for clarity.
    • 11 hrs · Like · 2
    •  
      Sumit Sharma Priey Ranjan .. one thing .. I was just checking out the topology with configuration. Regarding Root Bridge, which switch is acting as Root Bridge. Did we changed STP priority value on Switch 2 & Swtch 4 ?
    •  
      Priey Ranjan Yes.. We changed the priority value 0 for vlan 10 on sw2 and we also change the priority 4096 on sw4 for vlan 10..because reason is this for switch 3 both side Stp cost same then path decision will go on bridge Id.. Which have a lower..
      9 hrs · Unlike · 1
    •  
      Sumit Sharma It means simply, we have run PVST.
      For STP, related to VLAN 10, we make Switch 2 as Root bridge.
    •  
      Priey Ranjan Yup.. U might run rapid pvst
      9 hrs · Unlike · 1
    •  
      Sumit Sharma Priey Ranjan .. Good work done .. !!
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2 comments

  1. Hi all,
    I have practically observed this scenario in a live network where i had some doubt about the already configured design.The same situation was there that Switch A was acting as HSRP actve for a block of layer 2 switches and switch B was standby for that same block of switches but as per STP ( MSTP) swtch B was the root bridge for that block.
    After many discussions i nailed down the problem with layer 2 trace.Normally people run layer 3 trace or ping etc so it seems that all the traffic is exiting from Switch A which is HSRP Active but you can see clearly with a layer 2 trace that your Access switch is first forwarding traffic to the Root Bridge ( Switch B) and then finally to Switch A.
    Hope this helps, I can further clarify things if u needed.

    Liked by 1 person

    1. =================================================================
      Good to see .. very Logical approach ..
      Yes .. you are right .. Layer 2 Trace can be very useful, in this scenario.
      If you can share some output of scenario faced by you, that will also be useful.
      =================================================================
      I have two scenarios related to Layer 2 traceroute, for that click below,
      https://networkproxy.wordpress.com/2014/08/15/traceroute-layer-3layer-2-must-know-three-steps/
      =================================================================

      Like

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